Colonies of animals with congenital coagulation and platelet function defects are maintained for breeding purposes, genetic and physiologic studies, production of reagents for coagulation tests, and evaluation of hemostasis. These include dogs with hemophilia A, hemophilia B, hemophilia AB, von Willebrand's disease, factor VII deficiency, factor X deficiency, factor XI deficiency, dysprothrombinemia, thrombasthenic thrombopathia, and various combinations of these defects; fawn-hooded rats with hereditary platelet serotonin deficiency (storage pool disease); and Flemish Giant-Chinchilla rabbits with autosomal factor VIII deficiency and long bleeding times. Three new canine families with von Willebrand's disease and four cases of feline hemophilia are being studied. Heterologous antibodies to purified canine, rabbit, and porcine factor VIII are used to monitor levels of factor VIII-related antigen for research and diagnostic purposes. Studies of canine von Willebrand's disease are directed at the organs and cellular sites involved in the production, regulation, and release of factor VIII and at the nature of the factor VIII complex and the defects in bleeding time, platelet retention, and ristocetin-induced platelet aggregation. BIBLIOGRAPHIC REFERENCES: Dodds, W.J., Moynihan, A.C., Benson, R.E., and Hall, C.A. 1975. The value of age- and sex-matched controls for coagulation studies. Brit. J. Haematol., 29:305. Hall, C.A., London, A.R., Moynihan, A.C., and Dodds, W.J. 1975. Hereditary factors VII and IX deficiency in a large kindred. Brit. J. Haematol., 29:318. Dodds, W.J. 1975.